Apparatus and method for measuring noise, and recording medium

ABSTRACT

A noise measuring unit  24  measures a noise power based on an output from a digitizer  16  and the amplification factor of a limiter amplifier  12  when an output from a device under test  10  is supplied for the digitizer  16  through the limiter amplifier  12 . Since the output from the device under test  10  is supplied through the limiter amplifier  12 , the noise component is sufficiently amplified, the carrier component saturates, and thus, the noise measuring unit  24  easily measures the noise power. At this time, the output frequency of the device under test  10  is not multiplied, and thus, it is not necessary to use a down converter or a spectrum analyzer, the C/N ratio can be measured at a high speed or with a simple constitution.

This application is a 371 of PCT/JP01//08047 Sep. 17, 2001.

FIELD OF ART

The present invention relates to measuring the C/N ratio (Carrier toNoise ratio) of a signal provided from a DUT (Device Under Test).

BACKGROUND ART

Conventionally, the C/N ratio of a signal provided from a DUT (DeviceUnder Test) has been measured, and a system configuration for themeasuring is shown in FIG. 7.

The frequency of a signal Fs provided from a DUT 102 is multiplied byabout a few tens by a multiplier 104. The frequency of a signal Fs×Nprovided from the multiplier 104 is reduced by a down converter 106 downto a frequency which a digitizer 108 can process, and then, the signalis supplied for the digitizer 108. The digitizer 108 can measure the C/Nratio of the signal Fs×N provided from the multiplier 104. Note thatsince the C/N ratio is reduced by multiplying the frequency of thesignal Fs provided from the DUT 102, the reduced amount is obtained bycalculation, and the C/N ratio of the signal Fs provided from the DUT102 is obtained.

Alternately, the measuring system may be configured as shown in FIG. 8.Though this system is identical to the example above up to the processwhere the signal provided from the DUT 102 is multiplied by about a fewtens by the multiplier 104, the frequency of the signal provided fromthe multiplier 104 is not reduced, and is processed by a spectrumanalyzer 110. The C/N ratio of the signal Fs×N provided from themultiplier 104 can be measured by the spectrum analyzer 110. Note thatsince the C/N ratio is reduced by multiplying the frequency of thesignal Fs provided from the DUT 102, the reduced amount is obtained bycalculation, and then, the C/N ratio of the signal Fs provided from theDUT 102 is obtained.

However, since the frequency which the digitizer 108 can handle isgenerally about a few tens of MHz, the down converter 106 is necessaryin the system shown in FIG. 7. The down converter 106 which meets such ahigh frequency signal as supplied from the multiplier 104 is expensive,and its circuit is complex.

In the system shown in FIG. 8, since the processing speed of thespectrum analyzer 110 itself is generally slow, the overall processingspeed also is slow.

In view of the foregoing, the present invention has a purpose ofproviding an apparatus and the like which can measure the C/N ratioprovided from the DUT at a high speed or with a simple constitution.

DISCLOSURE OF THE INVENTION

According to an aspect of the present invention, a noise measuringapparatus includes: a limiter amplifying unit, that provides a signal tobe measured in a predetermined range; and a digital data convertingunit, that converts the output from the limiter amplifying unit intodigital data.

In the noise measuring apparatus constituted as described above, acarrier component in the output from the DUT is relatively largecompared with a noise component. Thus, if the limiter amplifying meansamplifies the output from the DUT, the noise component becomes larger.Additionally, since the signal after amplifying is provided in apredetermined range, the carrier component saturates, and does notbecome too large. Therefore, if the output from the limiter amplifyingmeans is converted into digital data by the digital data convertingmeans, since digital data with the increased noise component areobtained, measuring the noise component becomes easy. Consequently, thenoise component is measured at a high speed or with a simpleconstitution.

Note that the predetermined range generally means a one with determinedupper limit and lower limit. However, the range may have only adetermined upper limit or lower limit if necessary.

The noise measuring apparatus according to the present invention furtherincludes a noise measuring unit, that measures noise based on the outputfrom the digital data converting unit and an amplification factor of thelimiter amplifying unit.

The noise measuring apparatus according to the present invention furtherincludes a carrier digital data converting unit, that converts theoutput from the device under test into digital data.

The noise measuring apparatus according to the present invention furtherincludes an output switching unit, that supplies the digital dataconverting unit with the output from the limiter amplifying unit or theoutput from the device under test, wherein the digital data convertingunit also serves as the carrier digital data converting unit.

The noise measuring apparatus according to the present invention furtherincludes a carrier measuring unit, that measures the carrier based onthe output from the carrier digital data converting unit.

The noise measuring apparatus according to the present invention furtherincludes a noise measuring unit, that measures noise based on the outputfrom the digital data converting unit and the amplification factor ofthe limiter amplifying unit.

The noise measuring apparatus according to the present invention furtherincludes a C/N ratio calculating unit, that calculates a C/N ratio basedon a measured result of the carrier measuring unit and the noisemeasuring unit.

According to another aspect of the present invention, a noise measuringmethod includes: a limiter amplifying step of providing a signal to bemeasured in a predetermined range; and a digital data converting step ofconverting the output from the limiter amplifying step into digitaldata.

According to another aspect of the present invention, acomputer-readable medium has a program of instructions for execution bythe computer to perform a noise measuring process, the noise measuringprocess including: a limiter amplifying step of providing a signal to bemeasured in a predetermined range; and a digital data converting step ofconverting the output from the limiter amplifying step into digitaldata.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a constitution of a noise measuringapparatus 1 according to an embodiment of the present invention;

FIG. 2 is a drawing showing an operation of a limiter amplifier 12;

FIG. 3 are drawings showing an operation of a digitizer 16, and includea drawing (FIG. 3( a)) showing a form of sampling an output from a DUT10, and a drawing (FIG. 3( b)) showing a form of sampling an output fromthe limiter amplifier 12;

FIG. 4 are drawings showing a method of measuring power of a carriersignal, and include a drawing showing an output from the digitizer 16(FIG. 4( a)), a drawing showing separated carrier component and noisecomponent (FIG. 4( b)), a drawing showing the output from the digitizer16 transformed into the frequency domain (FIG. 4( c)), and a drawingshowing a relationship between the actual frequency and the power (FIG.4( d));

FIG. 5 are drawings showing a measuring method for noise power, andinclude a drawing showing the output from the digitizer 16 when it isassumed that the output from the limiter amplifier 12 is not limited(FIG. 5( a)), a drawing showing the output from the digitizer 16 whenthe output from the limiter amplifier 12 ranges from −L to L (FIG. 5(b)), a drawing showing the output from the digitizer 16 transformed intofrequency domain (FIG. 5( c)), and a drawing showing a relationshipbetween the actual frequency and the power (FIG. 5( d));

FIG. 6 is a flowchart showing an operation of the embodiment of thepresent invention;

FIG. 7 is a drawing showing a system constitution when the C/N ratio ofthe signal provided from the DUT is measured in prior art; and

FIG. 8 is a drawing showing another system constitution when the C/Nratio of the signal provided from the DUT is measured in prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

The following section describes an embodiment of the present inventionwhile referring to drawings.

FIG. 1 is a block diagram showing a constitution of a noise measuringapparatus 1 according to the embodiment of the present invention. Thenoise measuring apparatus 1 according to the embodiment of the presentinvention comprises a DUT (Device Under Test) 10, a limiter amplifier12, a switch 14, a digitizer 16, and a C/N ratio (Carrier to Noiseratio) measuring unit 20.

The DUT 10 receives a signal to be measured which is not shown, andprovides a signal corresponding to the signal to be measured.

The limiter amplifier 12 amplifies the output from the DUT 10, providesthe amplified output, and provides a boundary value of a range when thesignal after the amplifying exceeds the range. The limiter amplifier 12serves as limiter amplifying means. The following section describes theoperation of the limiter amplifier 12 while referring to FIG. 2. First,a signal of a sinusoidal wave with the amplitude of A₀ is supplied forthe limiter amplifier 12. It is assumed that the amplification factor ofthe limiter amplifier 12 is G. If the output from the limiter amplifier12 were not limited, the output would be a signal of a sinusoidal wavewith an amplitude of GA₀. Further, when the output from the limiteramplifier 12 is limited to a range from −L to L, if the absolute valueof the output exceeds L, the output is ±L, namely the boundary value ofthe output range of the limiter amplifier 12. When the absolute value ofthe output is L or less, the output remains unchanged. Namely, if theinput is A₀ sin ωt, the output from the limiter amplifier 12 is:GA ₀ sin ωt(−L<GA ₀ sin ωt<L),L(L<GA ₀ sin ωt), or−L(GA ₀ sin ωt<−L).

Note that in the example above, the upper limit (L) and the lower limit(−L) are specified for the output range of the limiter amplifier 12.However, if the output from the device under test 10 is always equal toor more than 0, it is only necessary to specify the upper limit (L) forthe range of the output from the limiter amplifier 12. Oppositely, ifthe output from the device under test 10 is always equal to or less than0, it is only necessary to specify the lower limit (−L) for the range ofthe output from the limiter amplifier 12.

Returning to FIG. 1, the switch 14 connects the output from the DUT 10or the output from the limiter amplifier 12 with the input to thedigitizer 16. The switch 14 has an input terminals 14 a and 14 b, and anoutput terminal 14 c. The input terminal 14 a is connected with theoutput from the DUT 10. The input terminal 14 b is connected with theoutput from the limiter amplifier 12. The output terminal 14 c isconnected with the input to the digitizer 16. The switch 14 connects theinput terminal 14 a and the output terminal 14 c with each other, or theinput terminal 14 b and the output terminal 14 c with each other.

The digitizer 16 converts the output from the switch 14 into digitaldata, and provides the data. When the switch 14 connects the inputterminal 14 a and the output terminal 14 c with each other, thedigitizer 16 converts the output from the DUT 10 into digital data. Atthis time, the digitizer 16 serves as carrier digital data convertingmeans. When the switch 14 connects the input terminal 14 b and theoutput terminal 14 c with each other, the digitizer 16 converts theoutput from the limiter amplifier 12 into digital data. At this time,the digitizer 16 serves as digital data converting means.

The following section describes the operation of the digitizer 16 whilereferring to FIG. 3. The digitizer 16 oversamples the output of the DUT10 or the output of the limiter amplifier 12. For example, FIG. 3( a)shows a form of sampling the output from the DUT 10, and FIG. 3( b)shows a form of sampling the output from the limiter amplifier 12 whenthe oversampling rate=4. The time interval of the sampling is ¼ of theperiod of the output from the DUT 10 or the output from the limiteramplifier 12. Namely, the frequency is four times. Note that thesampling of the output from the limiter amplifier 12 is conducted onlyin the neighborhood of the level 0 which is not clamped by the limiteramplifier 12. For example, the sampling is conducted only at points 100in FIG. 3( b).

While the digitizer 16 serves as the carrier digital data convertingmeans and the digital data converting means, a digitizer serving as thecarrier digital data converting means and a digitizer serving as thedigital data converting means may be provided independently.

The C/N ratio measuring unit 20 comprises a carrier measuring unit 22, anoise measuring unit 24, and a C/N ratio calculating unit 26.

The carrier measuring unit 22 measures the power of the carrier signalbased on the output from the carrier digital data converting means.Namely, it measures the power of the carrier signal based on the outputfrom the digitizer 16 when the digitizer 16 converts the output from theDUT 10 into the digital data.

The following section describes a measuring method for the power of thecarrier signal while referring to FIG. 4. FIG. 4( a) shows the outputfrom the digitizer 16 when the digitizer 16 converts the output from theDUT 10 into the digital data. As shown in FIG. 4( a), the output fromthe digitizer 16 is a signal of the carrier signal superimposed by aminute noise. It is assumed that the frequency of the carrier componentis fc. It is also assumed that the noise component has a constantfrequency, and the frequency of the noise component is fn. As a result,as shown in FIG. 4( b), the output from the digitizer 16 is divided intothe carrier component (frequency: fc) and the noise component (frequencyfn). When the output from the digitizer 16 is Fourier-transformed, andthe powers for the respective frequencies are obtained, there existpowers at the frequency fc and the frequency fn as shown in FIG. 4( c).If the power at the frequency fc is Pc, and the power at the frequencyfn is Pn, the power of the carrier frequency is Pc. Thus, the power ofthe carrier signal is obtained by Fourier-transforming the output fromthe digitizer 16, and obtaining the power at the frequency of fc. Notethat since the frequency of the noise component has a width, the actualrelationship between the frequency and the power takes the form shown inFIG. 4( d). However, the principle of obtaining the power of the carriersignal remains the same. Also, since the amplitude of the noise signalis small as shown in FIG. 4( d), it is difficult to measure it.

The noise measuring unit 24 measures the power of the noise based on theoutput from the digital data converting means. Namely, the power of thenoise is measured based on the output from the digitizer 16 when thedigitizer 16 converts the output from the limiter amplifier 12 into thedigital data.

The following section describes a measuring method for the power of thenoise while referring to FIG. 5. First, it is assumed that the frequencyof the carrier component is fc. It is also assumed that the noisecomponent has a constant frequency, and the frequency of the noisecomponent is fn. FIG. 5( a) shows the output from the digitizer 16 whenthe limiter amplifier 12 does not limit the output, and the digitizer 16converts the output from the limiter amplifier 12 into the digital data.Note that the output has already been divided into the carrier component(frequency: fc) and the noise component (frequency: fn) in the drawing.The noise component is multiplied by G/a compared with that of theoutput directly from the DUT 10. Note that (a) is an oversampling rateof the digitizer 16. However, since the carrier component is multipliedby G/a, the C/N ratio remains the same, and it is still difficult tomeasure the noise power.

FIG. 5( b) shows the output from the digitizer 16 when the output of thelimiter amplifier 12 ranges from −L to L, and the output from thelimiter amplifier 12 is converted into the digital data by the digitizer16. Though the carrier component saturates since the output is limitedto the predetermined range, the noise component does not saturate. Or,even if the noise component saturates, the degree of its saturation islower than that of the noise component. Note that though the L can bethe same as the amplitude A₀ of the carrier component, this value can beset arbitrarily as long as the limiter amplifier 12 is not damaged. Inthis way, when the carrier component saturates, the dynamic range formeasuring the noise power is multiplied by 2 G/a compared with the casewhere the noise power is measured based on the output from the DUT 10.

Then, after the output from the digitizer 16 is Fourier-transformed, andthe powers are obtained for the respective frequencies, certain powersexist at the frequency of fc and the frequency of fn as shown in FIG. 5(c). Here, the power at the frequency of fn is (G/a)·Pn. Thus, the powerof the noise is obtained by Fourier-transforming the output from thedigitizer 16, obtaining the power at the frequency of fn, and dividingthe obtained value by G/a. Note that since the frequency of the noisecomponent has a width, the actual relationship between the frequency andthe power takes the form shown in FIG. 5( d). However, the principle ofobtaining the noise power remains the same.

The C/N ratio calculating unit 26 obtains the C/N ratio based on themeasured results from the carrier measuring unit 22 and the noisemeasuring unit 24. Specifically, the C/N ratio can be obtained bydividing the result measured by the noise measuring unit 24 by theresult measured by the carrier measuring unit 22.

The following section describes the operation of the embodiment of thepresent invention while referring to a flowchart in FIG. 6. First, theinput terminal 14 a and the output terminal 14 c are connected with eachother in the switch 14, thereby supplying the digitizer 16 with theoutput from the DUT 10 (S10). The digitizer 16 converts the output fromthe DUT 10 into the digital data (S12). Then, the carrier measuring unit22 measures the power of the carrier signal based on the output from thedigitizer 16 (S14).

Then, the input terminal 14 b and the output terminal 14 c are connectedwith each other in the switch 14, thereby supplying the digitizer 16with the output from the limiter amplifier 12 (S20). The digitizer 16converts the output from the limiter amplifier 12 into the digital data(S22). Then the noise measuring unit 24 measures the power of the noisebased on the output from the digitizer 16 (S24).

Finally, the C/N ratio calculating unit 26 obtains the C/N ratio basedon the measured results from the carrier measuring unit 22 and the noisemeasuring unit 24 (S30). Specifically the C/N ratio is obtained bydividing the result measured by the noise measuring unit 24 by theresult measured by the carrier measuring unit 22.

With the present invention, the carrier component in the output from theDUT 10 is relatively larger than the noise component. Therefore, if thelimiter amplifier 12 amplifies the output from the DUT 10, the noisecomponent increases. In addition, when the signal after the amplifyingexceeds the predetermined range (from −L to L), since the output is setto ±L, the carrier component saturates, and does not increase toolargely. Thus, after the output from the limiter amplifier 12 isconverted into digital data by the digitizer 16, since the digital datawith the amplified noise component is obtained, measuring the noisecomponent becomes easy.

With the embodiment of the present invention, the power of the noisecomponent can be measured without multiplying the frequency of theoutput from the DUT 10. Thus, it is possible to measures the power ofthe noise component without a down converter or a spectrum analyzer.Therefore, the power of the noise component can be measured with aconstitution simpler than the down converter, or at a speed higher thanthe spectrum analyzer.

The embodiment described above can be realized as described below. Amedia reading apparatus of a computer comprising a CPU, a hard disk, andthe media (such as floppy disk and a CD-ROM) reading apparatus reads amedium recording a program for realizing the individual parts describedabove, and the program is installed on the hard disk. With this method,the function described above can be realized.

With the present invention, the carrier component in the output from theDUT is relatively larger than the noise component. Therefore, if thelimiter amplifying means amplifies the output from the DUT, the noisecomponent increases. In addition, when the signal after the amplifyingexceeds the predetermined range, since the output is set to the boundaryvalue of the range, the carrier component saturates, and does notincrease too largely. Thus, after the output from the limiter amplifyingmeans is converted into digital data by the digital data convertingmeans, since the digital data with the amplified noise component isobtained, measuring the noise component becomes easy. Consequently, thenoise component can be measured at a high speed or with a simpleconstitution.

1. A noise measuring apparatus, comprising: a limiter amplifying unitthat amplifies a signal to be measured to output an amplified signal ina predetermined range; and a digital data converting unit that convertsthe amplified signal into digital data, wherein the signal to bemeasured is outputted from a device under test and said predeterminedrange is determined so that a carrier component of the amplified signalsaturates and a noise component of the amplified signal does notsaturate.
 2. The noise measuring apparatus according to claim 1 furthercomprising a noise measuring unit that measures noise based on theoutput from said digital data converting unit and an amplificationfactor of said limiter amplifying unit.
 3. The noise measuring apparatusaccording to claim 1 further comprising a carrier digital dataconverting unit that converts the output from said device under testinto digital data.
 4. The noise measuring apparatus according to claim 3further comprising an output switching unit that supplies said digitaldata converting unit with the output from said limiter amplifying unitor the output from said device under test, wherein said digital dataconverting unit also serves as said carrier digital data convertingunit.
 5. The noise measuring apparatus according to claim 3 furthercomprising a carrier measuring unit that measures the carrier based onthe output from said carrier digital data converting unit.
 6. The noisemeasuring apparatus according to claim 5 further comprising a noisemeasuring unit that measures noise based on the output from said digitaldata converting unit and the amplification factor of said limiteramplifying unit.
 7. The noise measuring apparatus according to claim 6further comprising a C/N ratio calculating unit that calculates a C/Nratio based on a measured result of said carrier measuring unit and saidnoise measuring unit.
 8. A noise measuring method, comprising: a limiteramplifying step of amplifying a signal to be measured to output anamplified signal in a predetermined range; and a digital data convertingstep of converting the amplified signal into digital data, wherein thesignal to be measured is outputted from a device under test and saidpredetermined range is determined so that a carrier component of theamplified signal saturates and a noise component of the amplified signaldoes not saturate.
 9. A computer-readable medium having a program ofinstructions for execution by the computer to perform a noise measuringprocess, said noise measuring process comprising: a limiter amplifyingstep of amplifying a signal to be measured to output an amplified signalin a predetermined range; and a digital data converting step ofconverting the amplified signal into digital data, wherein the signal tobe measured is outputted from a device under test and said predeterminedrange is determined so that a carrier component of the amplified signalsaturates and a noise component of the amplified signal does notsaturate.